1. Field of the Invention
The present invention relates to decoders for 4QAM-NR and methods thereof, and in particular relates to decoders for 4QAM-NR with data interfered during transmission in a DMB-TH system.
2. Description of the Related Art
During data transmission with wireless technology, the data are encoded at a transmission terminal to avoid interference during the transmission process and data loss. However, should interferences occur during data transmission, after receiving the data by a receiving terminal, the receiving data would be rendered useless because of destruction of the data due to the interference.
In a DMB-TH system, the encoding methods are divided into 64QAM, 32QAM, 16QAM, 4QAM and 4QAM-NR according to characteristics of the data encoded at the transmission terminal. The 4QAM-NR encoding method at the transmission terminal released by the official transmission protocol is shown in FIG. 1. Presently, there is a need for developing a decoding method for 4QAM-NR.
Referring to FIG. 1, it shows the encoding method for 4QAM-NR in a DMB-TH system. An original data comprises 8 bits as X0˜X7, and the 8 bits are mapped to be 16 bits by a NR mapping, the mapping data are Y0˜Y7. As shown in FIG. 1, the 8-bit original data 11 (X0X1 . . . X7) are calculated according to mapping formula 12 at the transmission terminal (not shown), and the 8-bit original data 11 becomes 16-bit mapping data 13 (X0X1 . . . X7Y0Y1 . . . Y7; NR-code). Then, the data is transmitted by the form of mapping data 13 till mapping data 13 is received by the receiving terminal (not shown). Decoding operation is performed on mapping data 13 to recover the original data 11 for usage.
However, during data transmission with wireless technology, mapping data 13 may be interfered with during transmission, and the content of mapping data 13 may be changed from the original mapping data 13 due to the interferences. In this situation, the changed mapping data 13 will not be able to find the corresponding original data 11 via the mapping table of original data 11 and mapping data 13. Here, the changed mapping data 13 will require sorting and comparing to approximate the original data.
Because mapping data 13 have 16 bits, 65536 operations are required for priority sorting, thus, placing a heavy load on hardware requirement. Therefore, an important issue is to develop a method for decoding interfered and encoded 4QAM-NR data at a receiving terminal.